Digital cameras, and related digital camera modules that make up a digital camera, perform a white balancing operation upon capturing an image. A digital camera module also undergoes testing and calibration processes, such as white balance calibration, during manufacturing, and this includes digital cameras included in electronic devices such as mobile telephones.
Unlike the human eye, which has the capability to automatically adjust to lighting conditions to properly perceive white, as well as other colors, camera modules must be calibrated in advance so as to accommodate varying light sources. However, digital camera modules vary from camera module to camera module with respect to their spectral response characteristics and therefore, white balance calibration would be most accurate if each digital camera module were individually tested and calibrated. As one would understand, such a calibration process is time consuming and therefore also has an associated cost, thereby increasing the overall production costs associated with digital cameras.
White balance calibration under a given illumination source is accomplished by, for example, illuminating a known image reference surface (such as a standard white card) with a light source and measuring red, green and blue, that is, the R/G/B camera module's spectral responses with respect to red, green and blue wavelengths. Where one of the wavelengths exhibits a peak, or a higher amplitude than other wavelengths, according to measured R/G/B responses, a set of appropriate gains may be applied such that the overall spectral R/G/B responses are equalized with respect to all spectral wavelengths (i.e. colors). That is, adjustments may be made such that the camera module correctly “perceives” white for the given illumination source under calibration test. However, such response gain adjustments, which may also be referred to as a “gain adjustments scaling factors,” are specific to the light source tested, and do not apply to other light sources having different spectral characteristics. Therefore, testing time is further increased, due to the need to test each of the light sourced individually, in order to create a set of gain values scaling factors appropriate for that particular light source.
Therefore, what is needed are methods and apparatuses for reducing the test and calibration time, and therefore the cost, associated with calibration of digital camera devices.